The present invention relates generally to respiratory equipment and, in particular, to a pneumatically-operated gas demand apparatus coupled in interruptible fluid communication between a recipient and at least one source of a pressurized gas and adapted for controlling delivery of the pressurized gas to the recipient as the recipient inhales and exhales.
Many medical patients suffering from any one of a variety of lung ailments are often prescribed supplemental oxygen therapy so that the patient could breath oxygen-enriched air throughout the day and sometimes throughout the night. Earlier supplemental oxygen therapy employed a nasal cannula system operably connected between a tank of compressed oxygen and the patient""s nose. Oxygen was continuously delivered to the patient throughout the patient""s entire breathing cycle. This method of continuously delivering oxygen to the patient throughout the patient""s breathing cycle was considered wasteful because much of the oxygen dissipated into the ambient air environment. Better methods of delivering oxygen to the patient were later developed which included improved equipment that would only deliver oxygen to the patient during the inhalation phase of the patient""s breathing cycle. Usually, this improved equipment employed a demand valve which opened to deliver supplemental oxygen to the patient only when the patient inhaled. Numerous types of demand valves are well known in the prior art.
One such demand valve is described in U.S. Pat. No. 5,360,000 to Carter. This demand valve is compact, simplified and totally pneumatic. The demand valve which is coupled between a source of pressurized gas such as oxygen and the patient includes a valve body having a gas flow passageway and pneumatically-coupled sensing and slave diaphragms. The slave diaphragm is interposed in the gas flow passageway and prevents gas from flowing during the exhalation phase of the patient""s respiratory cycle. During inhalation, which is sensed by a sensing diaphragm, the slave diaphragm moves to open the gas flow passageway, thus permitting flow of gas to the patient. Although effective in delivering gas to a patient upon demand, this demand valve has an inherent problem. When the patient inhales to cause delivery of oxygen to patient, oxygen is also vented into the ambient air environment for as long as the slave diaphragm remains opened. This leads to wastage of oxygen which is the very problem that demand valves were designed to prevent.
Furthermore, this demand valve has an inherent deficiency of delivering gas to the patient in a continuous flow stream upon and during the inhalation phase. Unfortunately, the air remaining in the patient""s respiratory passageway, i.e., the nasal cavity and the throat, is first taken into the lungs upon inhalation. The oxygen-enriched air then follows the remaining air and only approximately one-half of the oxygen-enriched air ever reaches the lungs. The remaining one-half of the oxygen-enriched air remains in the patient""s respiratory passageway during the waning moments of inhalation and is the first to be exhaled therefrom during exhalation. It would be beneficial to the patient if this air remaining in the patient""s respiratory passageway after exhalation could be purged or otherwise enriched with oxygen before it is inhaled. Such an approach is utilized in U.S. Pat. No. 4,686,974 to Sato et al.
U.S. Pat. No. 5,666,945 to Davenport, the disclosure of which is incorporated herein by reference, describes a pneumatically-operated gas demand apparatus which overcomes many of the deficiencies of prior devices. The Davenport apparatus includes cooperating supply and sensing valves in interruptible fluid communication between a recipient (or patient) and at least a first source of pressurized gas. The supply valve includes a supply valve housing with a first diaphragm member disposed therein. Similarly, the sensing valve includes a sensing valve housing and a second diaphragm member disposed therein. The Davenport apparatus is constructed such that, when the recipient inhales, the second diaphragm member assumes a flow-causing position and the first diaphragm member assumes a flow-supplying position whereby pressurized respiratory gas is delivered to the recipient. When the recipient exhales, the second diaphragm member assumes a flow-stopping position and the first diaphragm member assumes a flow-blocking position, thereby preventing delivery of the respiratory gas to the recipient.
The pneumatically-operated gas demand apparatus of Davenport also includes a bolus chamber structure, a supply orifice element and a pilot orifice element. The bolus chamber defining a bolus chamber therein is disposed between and in fluid communication with a regulator mechanism and a supply chamber region of the supply valve. The supply orifice element having a supply orifice formed therethrough is disposed between the regulator mechanism and the bolus chamber structure. The pilot orifice element having a pilot orifice extending therethrough is disposed between a source of pressurized respiratory gas and the supply valve.
The bolus chamber functions as a repository or accumulator for a volume of pressurized respiratory gas which is discharged during inhalation and recharged during exhalation by the recipient. The bolus chamber enables the apparatus to deliver a high-flow pulse of oxygen to the recipient upon commencement of the inhalation phase of the recipient""s breathing cycle. The high-flow oxygen pulse advantageously enriches the air remaining in the recipient""s airway upon inhalation and, simultaneously therewith, purges some of the air from the recipient""s respiratory passageway. The Davenport device also delivers a continuous flow of oxygen immediately after delivery of the pulse of high-flow oxygen and for the remaining portion of inhalation whereby the recipient receives oxygen enriched respiratory gas throughout inspiration.
The intermittent gas delivery device of Davenport may also be used with a nebulizer. Pursuant to this modality, the high-flow pulse of oxygen delivered from the bolus chamber generates a fine mist of medicament-containing aerosol within the nebulizer which is inhaled by the recipient. The mist may thereafter be followed with a flow of pressurized respiratory gas for the remainder of inhalation.
In the Davenport device, the pulse volume is proportional to the supplied flow rate. Such a system works well in circumstances where the ratio of highest to lowest recipient demand flow rate is on the order of about three to about four to one. However, many patients have rather expansive demand flow ranges. Under these circumstances, the required flow ratio (which is an empirical ratio of the maximum to minimum demand flow rates) may become quite large. The flow requirements for some recipients, for example, may range from as low as about 0.5 lpm (liters per minute) for sedentary persons to as high as about 6 lpm for persons under physical stress. This maximum to minimum flow ratio would in turn require a pressure range of up to about 12:1 or more. Such a broad band of demand flow requirements impacts design and operation of the Davenport system in several significant ways.
First, the regulator mechanism must employ a high pressure regulator to reduce the high pressure supply gas to a workable level and a low pressure regulator to service the broad range of flow and pressure delivered by the system. The high pressure regulator must be capable of supplying respiratory gas at the higher pressure regions, and the supply (or pilot) valve must be reinforced to accommodate this higher pressure. In so doing, the dynamic performance of the supply valve (xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d timing, leakage flow, and the like) may be detrimentally affected. Second, an extremely small pilot orifice must be provided between the source of pressurized respiratory gas and a control region of the supply valve to ensure proper operation of the sensing valve. Third, the operating range of the low pressure regulator must be quite broad which may result in errors in the low pressure regulator and its adjustment mechanism that may become substantial at lower operational settings.
An advantage exists, therefore, for a pneumatically-operated gas demand apparatus capable of providing a high-flow pulse of pressurized respiratory gas upon commencement of the inhalation phase of a recipient""s respiratory cycle and which reliably operates in flow ranges from as low as about 0.5 lpm to as high as 6 lpm or more. The apparatus also preferably should be usable with a nebulizer to generate and deliver a medicament-containing aerosol to a recipient on demand as the recipient inhales and exhales while minimizing wastage of oxygen. It would be advantageous if this pneumatically-operated gas demand apparatus can deliver a high-flow pulse of oxygen to the recipient/patient upon commencement of the inhalation phase of the patient""s breathing cycle. Such a high-flow pulse of oxygen delivered upon commencement of the inhalation phase would enrich the air remaining in the patient""s respiratory passageway upon inhalation and, simultaneously therewith, purge some of this air therefrom before being inhaled. It would also be advantageous if this pneumatically-operated gas demand apparatus can deliver a continuous flow of oxygen immediately after delivery of the pulse of high-flow oxygen and throughout the remaining portion of inhalation.
There is a further need in the industry to provide a selective controller for a pneumatically-operated gas demand apparatus that can simultaneously regulate pressure and flow of gas administered by the apparatus. The pressure and flow controller should be easy to use, reliable and capable of administering one or more high pressure boluses of pressurized gas at the onset of a recipient""s inspiratory cycle and continuous flow for the remainder of the inspiratory cycle.
Published PCT Application No. WO 97/11734 describes an adjustable flow controller for a pneumatically-operated gas demand apparatus disposed between a conventional high pressure regulator and the supply chamber of the demand valve for selectively delivering gas at desired flow rates to the supply chamber. The flow controller is a rotor disk that is attached to a flow selector knob. The rotor disk is in fluid communication with the high pressure regulator and the supply chamber and includes a plurality of oxygen flow metering orifices of varying diameters. To select a desired flow rate, a user turns the selector knob until the appropriate orifice is aligned with the flow path leading to the supply chamber. If another flow rate is desired, the user turns the selector knob until another orifice of suitable diameter is brought into alignment with the path. A spring-biased ball and detent mechanism releasably retains the flow selector knob in each selected position.
The flow controller described in WO 97/11734 does not provide any additional pressure control of the gas beyond that provided by the high pressure regulator. That is, a recipient may receive gas at variable flow rates for each pressure established by the high pressure regulator. However, the flow controller cannot further modify the pressure set by the high pressure regulator. At certain flow rates or under certain therapeutic circumstances, it may be desirable to change the gas pressure to a level different from that established by the high pressure regulator without readjusting the setting of the high pressure regulator. The device described in WO 97/11734 does not provide this capability. Moreover, that device provides a constant volume bolus regardless of the flow setting. In addition, it takes longer for the bolus to recharge at lower flow rates. If a patient is taking short, quick breaths, the bolus does not have adequate time to recharge. Under those circumstances, the device would function in essence as if it were a constant flow device.
In addition, spring-biased ball and detent retention mechanisms such as that used to retain the rotor disk disclosed in WO 97/11734 are susceptible to wear. During use, the ball tends to become abraded by the spring as well as form a groove between the detents. The ball may thus become prematurely worn. Concomitantly, when sufficiently deep, the groove formed by the ball makes it difficult for a user to locate a desired detent and reduces a detent""s ability to retain the ball.
The commercially available version of the sensing valve diaphragm described in WO 97/11734 with a plurality off standoffs formed integrally with the surface thereof facing opposite the supply valve diaphragm. The standoffs prevent the sensing valve diaphragm from sticking in the open position responsive to a patient""s inhalation, i.e., they prevent the wasteful continuous respiratory gas flow situation the apparatus was designed to avoid. In addition, the standoffs reduce the distance the sensing diaphragm must travel into and out of its flow-causing and flow-stopping positions and thus improve the response time apparatus to the onset of a recipient""s inhalation and exhalation cycles.
The typical pneumatically-operated gas demand apparatus, including that described in and marketed under WO 97/11734, is an intricate arrangement of many cooperating components that are machined and assembled to close tolerances. However, no device can be manufactured to perfection (zero tolerance) and, indeed, the 0.010 inch (+/xe2x88x920.005 inch) dimensional tolerance normally allowed for many of the components of such apparatus is cumulative in nature. As a consequence, the apparatus may be up to several multiples of 0.010 inch out of ideal fit at many locations in the final assembly. In respect to the sensing valve potion of the device, these cumulative tolerance effects may be of such magnitude that the sensing valve diaphragm may have to travel farther than desired to reach its flow-causing and flow-stopping positions. The practical impact of a sensing valve diaphragm that has a considerable range of motion is that the response timing of the device may be detrimentally affected responsive to the user""s exhalation and inhalation. Hence, oxygen or other respiratory gas may be wasted as the recipient exhales because of the delay of the sensing valve diaphragm in assuming its flow-stopping position. Conversely, the recipient may not be sufficiently oxygenated or otherwise enriched with respiratory gas during inhalation because of the delay of the sensing valve diaphragm in assuming its flow-causing position.
A sensing valve diaphragm equipped xe2x80x9cfixed-heightxe2x80x9d standoffs, such as those formed on the commercially available version of the sensing valve diaphragm described in WO 97/11734, has better response timing than a sensing valve diaphragm without standoffs. However, a sensing valve diaphragm with integrally-formed standoffs may not provide sufficiently rapid response timing in situations where the apparatus is considerably out of ideal fit in the sensing valve region.
A further advantage exists, therefore, for a pneumatically-operated gas demand apparatus having a pressure and flow controller which is reliable, easy to operate and capable of providing variable gas flow rates and pressure levels in pneumatically-operated gas demand apparatus having zero, one or more than one bolus chambers. The apparatus should respond rapidly to the onset of a recipient""s inhalation and exhalation cycles regardless of how true the apparatus may be to ideal fit in the sensing valve region thereof. Preferably, the pneumatically-operated gas demand apparatus also should be usable with a nebulizer to generate and deliver a medicament-containing aerosol to a recipient on demand.
An object of the present invention is to provide a pneumatically-operated gas demand apparatus for coupling in interruptible fluid communication between a recipient/patient and at least one source of pressurized respiratory gas such as oxygen. The apparatus should be operable to control delivery of oxygen to the recipient/patient as the recipient inhales and exhales while minimizing wastage of oxygen.
Another object of the present invention is to provide a pneumatically-operated gas demand apparatus which can deliver one or more high-pressure boluses of oxygen to the recipient/patient upon commencement of the inhalation phase of the recipient/patient""s breathing cycle and a continuous flow of oxygen thereafter and throughout the remaining period of negative pressure defining the inhalation phase of the breathing cycle.
Another object of the present invention is to provide a pressure and flow controller which is reliable, easy to operate and capable of providing variable gas flow rates and pressure levels in pneumatically-operated gas demand apparatus having zero, one or more than one bolus chambers.
Another object of the present invention is to provide a pneumatically-operated gas demand apparatus that responds rapidly to the onset of a recipient""s inhalation and exhalation cycles regardless of how true the apparatus may be to ideal fit in the sensing valve region thereof.
Yet another object of the present invention is to provide a pneumatically-operated gas demand apparatus which is simple in design and compact.
A still further object of the present invention is to provide a pneumatically-operated gas demand apparatus which can be fabricated from readily available components or can be integrated into a unitary construction.
Accordingly, a pneumatically-operated gas demand apparatus of the present invention is hereinafter described. The pneumatically-operated gas demand apparatus is coupled in interruptible fluid communication between a recipient (or patient) and a first source of a pressurized first gas and is adapted for controlling delivery of the first gas to the recipient as the recipient inhales and exhales. In its broadest form, the pneumatically-operated gas demand apparatus, like that disclosed in U.S. Pat. No. 5,666,945 to Davenport, includes a supply valve and a sensing valve. The supply valve includes a supply valve housing and a flexible first diaphragm member. The supply valve housing defines a first interior chamber formed therein. The first diaphragm member is disposed within the first interior chamber and is connected to the supply valve housing in a manner to divide the first interior chamber into a supply chamber region and a control chamber region. The supply chamber region is in interruptible fluid communication with and between the first source of the first gas and the recipient and the control chamber region is in continuous fluid communication with either the first source of pressurized gas or a second source of a pressurized second gas. The first diaphragm member is operative to hermetically seal the supply chamber region and the control chamber region from one another and is operative to move between a flow-blocking position and a flow-supplying position.
The sensing valve includes a sensing valve housing and a flexible second diaphragm member. The sensing valve housing defines a second interior chamber formed therein. The second diaphragm member is disposed within the second interior chamber and is connected to the sensing valve housing in a manner to divide the second interior chamber into a venting chamber region and a sensing chamber region. The venting chamber region is in interruptible fluid communication with and between the control chamber region of the first interior chamber of the supply valve and an ambient air environment and the sensing chamber region is in continuous fluid communication with the recipient. The second diaphragm member is operative to hermetically seal the venting chamber region and the sensing chamber region from one another and is responsive, when the recipient inhales and exhales, to move between a flow-stopping position and a flow-causing position. When the recipient inhales, the second diaphragm member is in the flow-causing position thereby causing either pressurized first gas or second gas to flow from the control chamber region, through the venting chamber region and into the ambient air environment which, in turn, causes the first diaphragm member to be in the flow-supplying position thereby delivering the first gas from the first source of pressurized first gas to the recipient. When the recipient exhales, the second diaphragm member is in the flow-stopping position thereby preventing gas flow from the control chamber region, through the venting chamber region and into the ambient air environment which, in turn, causes the first diaphragm member to be in the flow-blocking position thereby preventing delivery of the first gas to the recipient.
The pneumatically-operated gas demand apparatus also preferably includes a multiple bolus chamber structure, a plurality of supply orifice elements and a pilot orifice element. The multiple bolus chamber structure defining a plurality of bolus chambers therein is disposed between and in fluid communication with a pressure and flow controller and the supply chamber region of the supply valve.
Pursuant to a preferred embodiment, a dual bolus chamber construction operates to distribute the flow range of the apparatus between first and second bolus chambers. This division of flow requirements provides an arrangement whereby even broad recipient demand flow ranges, e.g., about 0.5 lpm to 6 lpm or more, may be easily accommodated without negatively impacting the performance of the supply valve, the sensing valve or the regulator mechanism.
In a preferred embodiment, the apparatus includes a pressure and flow control device disposed between and in fluid communication with a high pressure regulator, one or more bolus chambers (if present) and the supply chamber region of the supply valve. The pressure and flow control device can modify the pressure set by the high pressure regulator and provide various flow rates during operation of the apparatus. At certain selected flow rates, the pressure and flow control device can change the gas pressure to a level different from that established by the high pressure regulator without readjusting the setting of the high pressure regulator.
Preferably, when a plurality of pressurized gases are conveyed by the apparatus, the first gas and the second gas are oxygen and, therefore, the first gas and the second gas are the same. With the first and second gases being the same, the at least one gas source may comprise a first source and a second source of pressurized gas that could also, but not necessarily, be the same. The first gas and the second gas can be different from each other. If so, the first source and the second source must also be different from one another. The first gas and the second gas are selected from either different ones or the same one of a group of gases consisting of oxygen, nitrous oxide, air and other types of gases.
The apparatus further preferably includes adjustable means for limiting the range of motion of the sensing valve regardless of how true the apparatus may be to ideal fit in the sensing valve region thereof. So constructed, the sensing valve may under all circumstances rapidly assume its flow-causing and flow-stopping positions responsive to the onset of the recipient""s inhalation and exhalation cycles.
Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the invention proceeds.